Manganese dioxide for primary cells



Patented Oct. 13, 1953 MAN GANE SEDIOXIDE FOR IRIMARY CELLS WilliamWaitman Gullett, College Park, Md., as: signer. to Manganese BatteryCorporation, Riverdale, Md., avcorporation Application March 5, 1951,Serial No. 213,949.

3 Claims.

This invention relates to the improvement of manganese dioxide forprimary cells. It relates particularly to the improvement of bulkdensity of otherwise satisfactory battery oxide. It has forits aim theimprovement of the bulk density of synthetic manganese dioxide withoutadversely afiecting its depolarizing properties.

It is Well known in the art that synthetic manganese dioxide such asthat made by oxidizing manganese carbonate has good depolarizingproperties but has a lower bulk density than natural African ore orbattery oxide prepared by the electrolytic process. For example, thebulk density of synthetic chemicaloxide variesfrom about 9-12 grams percubic inch while natural electrolytic ore varies from 18-22 grams percubic inch.

In this application the term bulk density will be used to designate thegrams per cubic inch of the oxide as determined by the Scott volumeter.

The initial capacity'of Le Clanche cells made from synthetic chemicaloxide is less than that of cells made from electrolytic oxidesubstantially in proportion to the lower apparent density.

I have found that if chemical synthetic oxides be densified inaccordance with my invention'that the initial capacity of Le Clanchecells made with them, is increased in proportion to, the densityincrease.

In Figure 1 there are illustrated typical discharge curves of Le Clanchecells. Inthi figure, curve A corresponds to a, cell made with asynthetic oxide, and curve B, to an identical cell made with the samesynthetic oxide densified in accordance with my invention. InFigure 2,comparative discharge curves are shown for identical alkaline cells.Curve 3 in this figure shows the discharge of a cell made With syntheticoxide, and curve A, the'discharge of a cell made afterdensification ofthis oxide by the practice of my invention. Details of the constructionof the cells of these illustrations will be found in Examples 1 and 3respectively.

In carrying. out the process of this invention I takesynthetic chemicalmanganese dioxide and mix it withgraphite. I then press themixture atatemperature of 450-650 F and a pressure of 10-50 tons per square inch.I then take the pellet so formed and crush it so that the product willpass a standard screen with 60 meshes to the linear inch and remain atleast in substantial proportion on a standard screen with 200 meshes tothe linear inch. The bulk density of such a product will be from -23grams per cubic inch and will show on test in a Le Clanche cell animprovement in initial capacity. approximately proportional to theincrease in bulk density.

I have found that the temperature and pressure of compacting thegraphitemanganese. dioxide mixture is critical. Even at the optimumtemperature of 600 F. there is substantially no improvement withpressures below 10 tons per: square inch. The maximum improvementintherange 450-650" F. is obtained at approximately tons per square inch andat pressures above tons per square inch there is a rapid falling off ofthe improvement in density.

There is substantially no improvement below 450 F. regardless ofpressure and a rapid d'eterioration above 650 F. The maximum improve--rnent is obtained at about 600 F. at all pressures within the range10-50 tons per square inch. The amount of graphite is also critical.

graphite- Smaller amounts down to 1% by.

weight give limited improvement and there is.

little or no improvement in density above 1.5% by weight of. graphite.

The size of composite graphite-manganese-di oxide particles produced bycomminutionisalso critical. particles sized to pass a standard screenhaving.

80 meshe to thelinear inch and remain on.- one. Particles intermediatein;

having. 100 meshes. size between those which all remain on a.- screenhaving meshes to the linear inch and those-of such size that by weightwill remain on a.

Having now described the general principles; or my invention, I willillustrateit by specific ex-- amples.

Example I I take synthetic manganese dioxide made by the oxidation offully crystalline manganese carbonate and leaching with 10% sulphuricacid. This manganese dioxide has an analysis as follows:

Available oxygen as per cent MnOz 89.1 Iotal manganese as per cent Mn58.5 Moisture as per cent H2O 1.9 Iron as per cent Fe 0.3 Silica as percent SiOz Nil pH 4.1

The. best results are obtained with by. weight of.

The maximum density is obtained with,

The crystal structure as determined by X-ray analysis was the so-calledgamma. This material had a bulk density when measured on Scott volumeterof 12 grams per cubic inch. This material when made into Size AA LeClanche cells showed a discharge through 300 ohms which has been plottedas curve a, Figure 1.

The same manganese dioxide was mixed with by weight micronized graphiteand hotpressed at 600 F. and 40 tons per square inch. The pressure wasapplied only instantaneously. The pellet produced in this way was cooledand comminuted to the following sieve analysis:

70% of the material would pass a screen with 100 meshes to the linearinch but not one with 125 meshes.

20% of the material would pass a screen with 125 meshes to the linearinch but not one with 150 meshes.

7% of the material would pass a screen with 150 meshes to the linearinch but not one with 200 meshes.

3% passed through a screen with 200 meshes to the linear inch.

This material showed a bulk density of 22.1

grams per cubic inch when tested in the Scott volumeter.

This material was then made into identical Le Clanche cells andsubjected to the same test as the unpressed manganese dioxide. Thedischarge curve is shown in curve I) of Figure 1.

The improvement of density and performance of the oxide treated inaccordance with my invention is clear.

Example 2 I take manganese dioxide such as is commercially available asa by-product of saccharin manufacture. This material is of high purityand is substantially amorphous. The apparent bulk density of thisproduct is 7-8 grams per cubic inch. This material is mixed with 10% byweight of micronized natural graphite and pressed at 500 F. and tons persquare inch.

The resulting pellets are comminuted so that the.

Example 3 I take oxide like that used in Example 1 and mix with 15% byweight of Acheson artificial graphite powder. I press this material at600 F. and 40 tons per square inch. The resulting pellets are comminutedso that all of the composite particles will pass a screen with 60 meshesto the linear inch but not one with 100 meshes. The bulk density of thisproduct was 15 grams per cubic inch. The product is made into adepolarizer for an alkaline cell by mixing with 2% by weight of powderednatural graphite and cold-pressing into a A diameter steel can at 40tons per square inch. The electrolyte used was 30% KOH and the anode acompressed pellet of granular amalgamated zinc. This cell was dischargedthrough a constant resistance of 300 ohms. A discharge curve for such acell is shown in curve a, of Figure 2. In curve b, Figure 2, is shownthe discharge curve of an identical cell made with the oxide as mixedwith 15% Acheson artificial graphite powder and coldpressed into thediameter steel can at 40 tons per square inch. This cell was alsodischarged through a constant resistance of 300 ohms.

What is claimed is:

1. The method of producing composite particles of chemical syntheticmanganese dioxide and graphite having a bulk density of 1523 grams percubic inch which includes the steps of mixing chemical syntheticmanganese dioxide with 1-15% by weight graphite powder, pressing themixture at a temperature between 400 F. and 650 F. and a pressure of10-50 tons per square inch, cooling the pellet so formed, andcomminuting it so that the resulting particles will all pass a standardscreen having 60 meshes to the linear inch and at least by weight of theparticles will remain on a screen having 200 meshes to the linear inch.

2. The method of improving the bulk density of synthetic manganesedioxide without impairing its depolarizing properties which includes thesteps of mixing chemical synthetic manganese dioxide with 1-5% by weightgraphite powder, pressing the mixture at a temperature between 400 F.and 650 F. at a pressure of 10-50 tons per square inch, cooling thepellet so formed and comminuting it so that the resulting particles willall pass a standard screen having 60 meshes to the linear inch and atleast 80% by weight of the particles will be larger in average diameterthan the original manganese dioxide.

3. The method of making a depolarizer for primary cells which includesthe steps of mixing synthetic manganese dioxide having a gamma structurewith 1-5% powdered graphite, heating to 400-600 F., pressing the mixturewhile at this temperature at 10-40 tons per square inch, thencomminuting the resultant pellet to obtain particles which will all passa standard screen having at least 60 meshes to the linear inch.

WILLIAM WAITMAN GULLETT.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 642,414 Bachmann et a1. Jan. 30, 1900 1,272,406 Ellis July 16,1918 1,293,272 Wells Feb. 4, 1919 1,296,700 Ruhofi Mar. 11, 19191,637,433 Yngve Aug. 2, 1927 1,724,886 Peiler Aug. 13, 1929 2,091,569Ridgway et a1 Aug. 31, 1937 2,208,185 Goudge May 27, 1939 2,307,301Hileman Jan. 5, 1943

1. THE METHOD OF PRODUCING COMPOSITE PARTICLES OF CHEMICAL SYNTHETICMANGANESE DIOXIDE AND GRAPHITE HAVING A BULK DENSITY OF 15-23 GRAMS PERCUBIC INCH WHICH INCLUDES THE STEPS OF MIXING CHEMICAL SYNTHETICMANGANESE DIOXIDE WITH 1-515% BY WEIGHT GRAPHITE POWDER, PRESSING THEMIXTURE AT A TEMPERATURE BETWEEN 400* F. AND 650* F. AND A PRESSURE OF10-50 TONS PER SQUARE INCH, COOLING THE PELLET SO FORMED, ANDCOMMINUTING IT SO THAT THE RESULTING PARTICLES WILL ALL PASS A STANDARDSCREEN HAVING 60 MESHES TO THE LINEAR INCH AND AT LEAST 80% BY WEIGHT OFTHE PARTICLES WILL REMAIN ON A SCREEN HAVING 200 MESHES TO THE LINEARINCH.